Retroreflective sheeting and methods for making same

ABSTRACT

A retroreflective relatively flexible laminate sheet construction has a thermoplastic web with a smooth light-receiving first side and a second side coextensive with said first side. A retroreflective pattern is formed on the second side. A slurry of granular material is deposited on the second side to cover selected portions of the formed pattern with remaining portions of the formed pattern devoid of the granular material, and said slurry is dried or cured to produce a well-defined pattern. A layer of backcoating material is deposited on the second side to overlay the granular material, the backcoating material contacting the thermoplastic web where no granular material has been deposited, thereby encapsulating the granular material between the second side and the backcoating layer. An added, outer layer provides additional weather protection for the thermoplastic web. Methods are detailed to manufacture the laminate, and compositions of backcoating mixtures also are disclosed.

This application is a continuation-in-part of copending U.S. applicationSer. No. 640,009, filed Aug. 10, 1984, entitled "RetroreflectiveSheeting and Methods for Making Same", which was a continuation-in-partof U.S. application Ser. No. 533,068, filed Sept. 19, 1983, both nowabandoned, and assigned to the same assignee as the prior application.

BACKGROUND OF THE INVENTION

Retroreflective sheeting has particular use in making highway signs,street signs and the like, and is now employed extensively. The Federalgovernment has recognized two primary types of retroreflective sheeting:glass bead and cube-corner. Such approved sheeting materials are foundin a specification entitled "FP-79", published by the U.S. Department ofTransportation, Federal Highway Administration. Specification FP-79presently has been adopted as a purchasing standard by many statehighway departments, and it sets forth certain minimum specificationswhich must be met by retroreflective sheeting of the cube-corner type.Included among the specified characteristics are those for reflectivity,color, flexibility of material and resistance to cracking andweathering.

Cube-corner type reflector elements generally provide a higher specificintensity at 0.2° observation angle and 0° entrance angle than do glassbead type reflector elements, but, to applicant's knowledge, no onesuccessfully has furnished a sheeting material in commercial quantitieswhich generally will meet the requirements for the Class IIB sheetingset forth in the aforementioned FP-79 specification. It therefore is aprimary object of the present invention to provide a unique sheetingproduct which will substantially meet such specified criteria and whichcan be produced in accordance with the novel methods disclosed herein inan economical fashion and in commercial quantities.

Retroreflectivity is achieved by cube-corner type reflector elementsprimarily through the principle of total internal reflection. It is wellknown that any surface contact made by another material with the facesof the cube-corner elements generally has a deleterious effect on thereflectiveness of the reflector element.

However, when all of the element faces are metallized, or mirrored,then, rather than relying upon total internal reflection,retroreflection is achieved by specular reflection from the mirroredfaces. Generally, metallizing will provide a grayish or black colorationunder certain daylight onditions vis-a-vis unmetallized cube-corner typeelements.

The present invention relates generally to methods and apparatus forproducing retroreflective sheeting constructins and, more particularly,to methods and apparatus for producing a flexible laminate sheetingconstruction including an upper thermoplastic sheet, the reverse ofwhich is provided with a repeating, retroreflecting pattern of fine orprecise detail, a backcoating to protect the formed pattern, and aselectively applied intermediate layer allowing bonding of thebackcoating to overlay the formed pattern on the thermoplastic sheetwhile preserving and enhancing the retroreflective properties of boththe formed pattern and the laminated sheet. More precisely, the presentinvention is applicable to the production of cube-corner typeretroreflective sheeting laminates.

Within the art of designing reflectors and retroreflective material, theterms "cube-corner" or "trihedral," or "tetrahedral" are recognized inthe art as describing structure or patterns consisting of three mutuallyperpendicular faces, not limited to any particular size or shape of thefaces, or the orientation of the optical axis of the cube-cornerelement. Each of the cube-corner faces can assume a different size andshape relative to the others, depending upon the angular reflectiveresponse characteristics desired, and the cube forming techniquesemployed.

Examples of prior cube-corner type reflectors may be found in U.S. Pat.No. 1,906,655, issued to Stimson, and U.S. Pat. No. 4,073,568, issued toHeasley. Stimson shows reflex light reflector including an obverse faceand a reverse light-reflecting face consisting of a plurality ofcube-corner type reflector elements with each such element having threemutually perpendicular surfaces adapted for total internal reflection oflight impinging thereof from the obverse face. Heasley describes acube-corner type reflector in the form of a rectangular parallelpiped.

It long has been desired to obtain the benefits of cube-cornerreflective properties in the form of fexible sheeting. As noted above,one advantageous aspect of such sheeting is in the manufacture ofhighway and street signs, markers and the like, where graphics areprinted, painted, silk-screened or otherwise applied to a highlyreflective substrate mounted to a flat, stiff, supportive surface.Flexible retroreflective sheeting, when used as such a substrate, can bestored and shipped while wound onto rolls, and can readily be cut orotherwise formed into the desired shape and size required for aparticular application. The reflective nature of the sheeting allowssuch signs, markers, and the like to reflect light from a vehicle'sheadlights, permitting the item to be read by the driver, withoutrequiring a permanent light source to illuminate the sign or marker.

Production of such retroreflective sheeting has been made practicable byapparatus and methods to form precise cube-corner patterns in greatlyreduced sizes on flexible thermoplastic sheeting. Desireably, suchsheeting may then be assembled in the form of self-adhesive laminates.

Others have recognized the desireability of producing retroreflectivethermoplastic material in sheet form. U.S. Pat. Nos. 2,310,790,2,380,447, and 2,481,757, granted to Jungersen, described and teach theshortcomings of previously-known reflectors manufactured from glass, andthe advantages inherent in providing a reflective material in a lessfragile and more flexible sheet form. While so suggesting, it is notknown if Jungersen in fact ever commercialized any product disclosed insuch patents.

In U.S. Pat. Nos. 4,244,683 and 4,332,847 issued to Rowland, thedesirability of manufacturing cube-corner retroreflective sheeting in acontinuous, nonstop process is presented, but the approach selected byRowland is a "semi-continuous" process (Rowland U.S. Pat. No. 4,244,683,column 2, lines 18-38), presumably so-called because the processrequires frequent repositioning of the molding plates.

In U.S. Pat. No. 3,187,068, issued to DeVries, et al., continuousproduction of reflective sheeting is disclosed, utilizing encapsulatedglass microspheres as the reflecting medium. DeVries, et al. describesthe application of a pressure-activated adhesive layer to such sheetingto enable attachment of sheeting setments to selected surfaces.

In U.S. Pat. No. 3,649,352, issued to Courneya, a beaded sheetingconstruction is described, portions of which become reflective whenheate, and which includes a pressure-activated adhesive layer allowingattachment of the sheeting construction to other articles.

Palmquist, et al. U.S. Pat. No. 2,407,680 teach the utilization of glassmicrospheres of beads included as the reflective elements in flexiblesheet forms; Tung, et al., in U.S. Pat. No. 4,367,920, also describes alaminated sheet construction using glass microspheres as the reflectiveelements.

A common problem in the construction of reflective laminate sheeting isto find means to bond the layers firmly together in a way whichpreserves the required retroreflective qualities of the reflectiveelements selected for use. An example of prior effects to solve thisproblem with respect to glass microspheres may be seen in U.S. Pat. No.3,190,178, issued to McKenzie, wherein a cover sheet or film is securedover exposed glass microspheres by use of die elements which force aportion of the material in which the glass microspheres are embeddedinto contact with the cover sheet. The die elements thus create a gridpattern on the resulting sheeting construction, with each grid forming aseparate cell. Within each cell, an air space is maintained between themicrospheres and the cover sheet, and incident light traverses the coversheet and the air space to be retroreflected by the embeddedmicrospheres.

Holmen, et al., U.S. Pat. No. 3,924,929, teach a cube-corner type upperrigid sheet having upstanding walls, or septa, integrally formed as partof the cube pattern. The septa extend to form a regular geometricpattern of individual cells, with the septa extending at least as farfrom the upper sheet as the cube-corner elements. A particulate packingmay be used to fill each of the cells, and a backing sheet is thenattached to the rear of the upper sheet, with the septa service as theattachment sites. Holmen, et al. use relatively large cube-cornerelements fashioned as rigid sections bound to a flexible back, and haslimited flexibility in use.

In McGrath, U.S. Pat. No. 4,025,159, the cellular concept is describedwith respect to cube-corner type retroreflective sheeting, through us ofdies to force a carrier film into contact with the reverse side of thecube-corner sheeting. The carrier film must then be cured with radiationto bind it to the cube-corner sheeting and, as in McKenzie, theresulting cells include an airspace extending between the carrier filmand the reverse side of the cube-corner sheet. The air cell structureapparently was intended to provide a hermetically sealed cell, avoidingthe need for metalizing the cube-corner elements, and providing anair/thermoplastic interface to enhance retroreflection.

None of the foregoing teach the assembly of molded or embossedcube-corner type retroreflective sheeting into self-adhesive laminateswhich protect and enhance the reflective properties of the sheetingwithout requiring the use of dies or of integrally-molded septa or wallsincluded as part of the cube pattern. Further, none of the foregoingpermits the material to benefit from encapsulated sections ofcube-corner elements while enhancing and substantially meeting therequirements specified in the aforementioned DOP FP-79 Specification.

BRIEF DESCRIPTION OF THE INVENTION

A thermoplastic sheet or web is provided on its reverse side with aretroreflective cube-corner type pattern. A thin layer of a liquidvehicle or solvent containing hydrophobic granular material (such assilica treated with silanes) is deposited on the reverse side of theweb, as by screen printing, in a pettern leaving selected sites devoidof granular material. The web is then dried to drive off the solventand, thereafter, a water-based backcoating is applied over the granularmaterial pattern, with portions of the backcoating being in directcontact with the thermoplastic web at those sites on the web devoid ofgranular material. Thereafter, the backcoating is dried or cured, and alayer of adhesive such as pressure-sensitive or heat-activated adhesiveis applied thereto. This procedured thus enables the assembly ofpatterned web material into laminates which include an activatedadhesive layer while protecting the retroreflective properties of theprecisely formed cube-corner pattern.

A thin layer of a hydrophobic silica mixture is then screened or sprayedonto the embossed reverse surface of the laminated thermoplastic web ina diamond-like pattern, and is thereafter dried. A water-basedbackcoating mixture of certain formulation is next deposited over thesilica layer to encapsulate the silica and to contact the thermoplasticsheet where no silica was deposited. The backcoating then is heat driedand/or cured to form a continuous film. A pressure-sensitive orheat-activated adhesive then is applied to the cured backcoating layer,with the adhesive protected by a release sheet which is removed when thelaminate is applied to an object.

In the preferred embodiment, an outer protective layer of thermoplasticmaterial, used to provide additional weather resistant properties, issecured to the thermoplastic web on the side opposite from that uponwhich the retroreflective pattern is formed during or before the cubeforming process.

The completed laminate is then cut, trimmed, or otherwise shaped forapplication to supporting surfaces, such as street or highway signs, andgraphics or other indicia may thereafter be painted, printed,silk-screened, or otherwise affixed to the uppermost surface of thelaminate, thus producing a readily and easily constructed highlyretroreflective finished product.

These and further aspects of the present invention will become moreapparent upon consideration of the accompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged perspective and somewhat schematic view of onepreferred aspect of the retroreflective sheeting of the presentinvention as a completed construction;

FIG. 2 is a view along line 2--2 of FIG. 1;

FIG. 3 is a greatly enlarged plan view illustrating a section of theformed surface of reflective sheeting comprising one aspect of thepresent invention;

FIG. 4 is a somewhat schematic and symbolic view of the processes andmachinery utilized in a preferred aspect of the present invention;

FIG. 5 is a plan view of one form of screen pattern used to apply thehydrophobic granular layer of the present invention;

FIG. 6 is an enlarged view, in partial detail, of an individual cell ofthe sheeting of the present invention; and

FIG. 7 is an enlarged perspective view illustrating a second preferredembodiment of the retroreflective sheeting of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIG. 3, the numeral 10 indicates generally a segment ofcube-corner type retroreflective themoplastic web used in forming thelaminate of the present invention. As seen in FIG. 3, there is depictedthe rear surface of a portion of flexible retroreflective sheeting 12fashioned from transparent thermoplastic material in web form which hasformed thereon, preferably by embossing, a retroreflective and repeatingpattern of cube-corner reflector elements characterized by cube faces14, 16 and 18. In a preferred aspect of such sheeting, sheet 12 isformed from an impact-modified acrylic material having UV inhibitors orabsorbers added thereto, and which, prior to embossing, had parallelfront and back surfaces and was initially on the order of about 0.006inches thick. One such material is know as Plexiglas DR, sold by theRohm and Haas Company.

The cube-corner pattern formed on sheeting 12 is formed in an opticallyprecise, finely-detailed pattern. For example, as seen in FIG. 2, thedepth to which the cube-corner pattern is embossed onto sheet 12 may beon the order of 0.00338 inch, (dimension X). As shown at dimension Y inFIG. 3, the cubes formed on sheet 12 may be spaced apart by a distanceon the order of about 0.0072 inch, for the depth as shown at X as setforth above. While the cube pattern shown in FIG. 1 illustrates cubesformed with their optical axes normal to the face of sheet 12, it is tobe understood that other versions and patterns may also be utilized asforming the retroreflective web of the laminate of the presentinvention.

Referring now to FIG. 1, the numeral 20 indicates generally a roll ofretroreflective laminate 22 manufactured in accordance with preferredaspects of the present invention to be described hereinbelow. As hereinshown, laminate 22 is rolled onto a core 24. A thermoplastic web 26having a front or obverse surface 28 and a rear or reverse surface 30upon which is embossed the cube-corner type retroreflective pattern isillustrated in FIG. 3. The thermoplastic web 26 may be on the order ofabout 6 mils (0.006 inch) in thickness.

Bonded to the reverse surface 30 of the thermoplastic web 26 isbackcoating or film 32. In a preferred aspect of the present invention,a hydrophobic granular silica material 34 is interposed between thebackcoat film 32 and the reverse side 30 in a manner to be describedhereinbelow.

In accordance with a preferred embodiment of the present invention, alayer of adhesive 36 is bonded to a release sheet 38 in a presentlywell-known fashion, and is thereafter bonded to cured backcoat film 32in order to provide a finished laminate 22 which includes apressure-sensitive or heat-activated adhesive layer 36 applied tosheeting 12 in a manner which preserves the retroreflective qualitiesand properties of the cube-corner pattern embossed thereon. The releasesheet 38 is used to protect adhesive layer 36 until it is desired toapply laminate 22 to a given surface.

FIG. 4 shows, in schematic form, a preferred arrangement of equipmentand sequence of operations to produce a retroreflective sheetinglaminate of the type shown in FIG. 3.

The application of adhesive directly to the reverse side of acube-corner embossed thermoplastic web 26 will cause undesirable andunacceptable loss of retroreflective capability. This arises from thecontact of the adhesive material with the obverse side of embossedthermoplastic web 26, i.e., the filling of the "valleys" formed by theembossed pattern and the subsequent interface formed between substancesthat are too similar in refractive indices to produce adequateretroreflection, so the transparent film can no longer utilize thephenomenon of total internal reflection to efficiently effectretroreflection of light. To solve this problem, a substantial portionof the cube-corner pattern either must be hermetically sealed with anair space between the back wall and the cube-corner elements, or thecube-corner elements must be backed in a way which would preserve theretroreflective properties of the formed web while providing sites forfirm attachment of an adhesive layer (or other adhesive material).Without such protection, and without such attaching sites, the use of,and effectiveness of a retroreflective embossed web is seriouslycompromised and curtailed.

Unexpectedly, use of hydrophobic granular materials has been found toafford such protection of optical properties. Among such materials arexylenated glass particles, powdered silicone rubber, and silane-treatedsilica.

As part of the present invention, it has been found that a hydrophobicsilica mixture consisting principally of amorphous silica treated withsilanes, when used to fill the valleys formed by the embossed pattern,preserves the retroreflective properties of the formed pattern for mostpractical purposes. Again, it is not known precisely why this effectobtains: it has been theorized that the point contact of granules withthe reverse face of the embossed thermoplastic web acts to preserve theretroreflective properties of the pattern, perhaps by preserving asufficient air interface with the reverse side of the cube-cornerpattern. However, the present invention obtains excellent results evenwhere the primary silica particles used are significantly smaller than,for example, the particles discussed in prior art patents such asHolmen, et al., U.S. Pat. No. 3,924,929.

Use of such silica offers advantages such as low price, easyavailability, and ease and precision of formulation. It further providesunique color and reflective characteristics to the film which improvesthe appearance of the film even relative to the glass bead typesheretofore commonly used.

As discussed hereinabove with respect to the Holmen, et al. reference,others have attempted to solve the problem of loss of reflectivity byproviding upstanding walls or septa as part of the rigid molded frontface pattern, with the septa forming individual pockets for theapplication of granular compounds having particle sizes far in excess ofthe silica particles used in the present invention. The disadvantages tosuch an approach, particularly with respect to the cube-corner typeembossed pattern utilized in the present invention are manifest. Use ofrigid septa limits the size and shape of the cell. A separate mold mustbe formed for each type of retroreflective sheeting requiring a cellsize other than that formed in the original mold. What is meant by theterm "cell size" is the area bounded by or closed off by the walls toform a single pocket for the granular backing material.

Formation of such septa in a relatively rigid mold pattern manufacturedto as fine and precise a degree of detail as that shown in the presentinvention also may cause problems with respect to stripping the formedthermoplastic web from the forming tool. This may particularly be aproblem where the septa or walls extend inwardly into the mold to adistance greater than the depth of the cube-corner pattern.

A preferred embodiment of the present invention includes the mixing of ahydrophobic silica mixture using hydrophobic silica, organic solvents,and thickeners, and the application of this mixture, while in a liquidform, to the reverse side of the formed thermoplastic web in a desiredpattern. One advantage of the present process and product is that thepattern can conveniently be changed to effect changes in reflectivecapability of the film, without changing the tools used in forming theembossed web. Thereafter, the partially coated or imprintedthermoplastic web is passed throught a drying oven which drives off thesolvents used to form the mixture, thereby drying the pattern on thethermoplastic sheet. The pattern in which the silica is applied to thethermoplastic web leaves selected portions or sites on the formed faceof the thermoplastic web devoid of silica.

Referring now to FIG. 5, the numeral 40 indicates generally such aselected pattern. Each runner or path 42 represents an area on thereverse surface of thermoplastic web 26 where no silica has beendeposited. Each square or diamond-shaped area 44 represents an area onthe surface of thermoplastic web 26 onto which the silica misture hasbeen deposited.

As seen in FIG. 6, the actual percentage of area covered by the silicamixture is determined by the thickness or width of each runner or path42, and the pattern selected for deposition of the silica, with the cell44 having an area bounded by the runners 42, and fully available for thereception and retroreflection of incident light by the embossedretroreflective patterns shown partially at 46.

Referring now to FIG. 4, it may be seen that thermoplastic web 26 may bedrawn directly from an associated forming machine (not hereinspecifically shown) in a continuous process, or may be drawn from aseparate supply reel onto which the embossed web 26 has been wound (notherein specifically shown). If desired, web 26 may be supported by abacking sheet (not herein specifically shown) coextensive with obverseface 28, leaving reverse surface 30 exposed.

It should be noted that reference to web 26 also includes reference to alaminate formed by web 26 and a backing sheet such as describedhereinabove.

Web 26 is drawn by, for example, powered rollers (not hereinspecifically shown), to silica mixture application station 48. As hereindiagrammatically shown, a preferred means and method of applying thesilica mixture to web 26 may be accomplished through use of ascreen-printing drum 50 which has mounted about the outer peripherythereof, a metal screen formed to provide the shape or pattern to whichit is desired to apply the silica mixture. The mixture is forced underpressure from the interior of screen-printing drum onto the reverse side30 of the thermoplastic web 26. As herein shown, the web 26 is direct byidler roller 52 to pass between the screen-printing drum 50 and abacking roller 54.

A preferred form of the apparatus utilized to apply the silica mixtureat application station 48 consists of a drum printer manufactured byStork Brabant BV of Boxmeer, Holland, of the type having a drum withelectroformed mesh screens over which a photo-resist pattern (such asused for conventional silk screen) may be mounted, with a screen patternproviding a diamond cell size in the range of from about 0.096 inch to0.300 inch, and a runner or cell wall width of from about 0.010 inch toabout 0.050 inch. Variations in the shape of the cells, pattern repeatof the cells, and width of the runners may be accomplished by changingthe printing screen used on screen-printing drum 50. Also, the width ofthe web may be of various sizes, and the printing screens used will beof a compatible width.

In its preferred form, the silica mixture is made from a hydrophobicsilica such as that manufactured by the Pigments Division of Degussa, ofFrankfurt, West Germany, under the trade designation Sipernat D10. Apreferred composition of the mixture includes hydrophobic silica in amixture containing approximately 98 percent silane-treated silicondioxide (SiO₂); 0.8 percent sodium oxide (Na₂ O), and 0.8 percent ofsulfur trioxide (SO₃); a non-polar aliphatic hydrocarbon solventcarrier; a polar solvent; and, where desired or required, a thickeningagent. It has been found that certain types of mineral spirits may havedeleterious effects upon the preferred web material. One aliphaticnon-polar hydrocarbon solvent successfully used is low odor mineralspirits, and a workable mixture has been created through use of anorganic alcohol, preferably n-butanol, as the polar solvent material. Asmectite clay-based thixotropic thickener also may be used in varyingamounts to produce a well-defined screen-printed pattern of the silicaslurry on the embossed thermoplastic web.

In its preferred embodiment, the primary particle size of the silica isabout 18 nanometers, and the agglomerated particle size of thehydrophobic silica in its final form is about 5 microns. However, itwill be understood that the only critical limination on the particlesize is such that the area in which it is deposited will besubstantially impervious to the backcoating material 32, whereby thebackcoating material is unable to penetrate the hydrophobic silica andinteract with the cube-corner pattern except in those areas devoid ofthe silica.

The particular combination of solvents and thickeners is important tosatisfactory deposition and definition of the silica in a precise andaccurate pattern. Screen printing of particulate material commonlyrequires use of resins or other binders to hold the deposited particlesin place. A resin or binder cannot however be used in this instancebecause of the adverse effect on reflectivity of the web because ofrefractive index similarities.

Another important consideration is the rheology, or flow characteristicsof the silica slurry as it is forced through the printing screen. Theslurry must "relax", or thin as it is forced through the screenapertures, and thereafter regain sufficient viscosity to retain awell-defined pattern with good leveling qualities and appearancecharacteristics. Yet another consideration is use of a solvent vehiclewhich obtains the aforementioned qualities without attacking ordegrading the thermoplastic web upon which the retroreflective patternis formed.

Use of polar solvents, such as n-butanol, enables the slurry to maintainan increased concentration of solids (silica). Such solvents, however,react with the thermoplastic material used to form the web. Non-polarsolvents, such as low odor mineral spirits, preserve the embossed web,yet do not act to provide a satisfactory silica pattern. Therefore ablend of polar and selected non-polar solvents has been found to beuseful in carrying enough solids without degrading reflectivity ordegrading the web.

Preferably, the hydrophobic silica is present in proportions rangingfrom about 15 percent to about 35 percent by weight, the non-polarsolvent carrier is present in amounts ranging from about 40 percent toabout 70 percent, the polar solvent is present in amounts ranging fromabout 10 percent to about 30 percent, and the thickening agent may bepresent in amounts from about 2 percent to about 8 percent. Onepreferred formulation of the silica mixture includes 32 percent byweight Sipernat D10 hydrophobic silica, 48.9 percent low odor mineralspirits, 15.6 percent n-butanol, and 3.2 percent thickener. It has beenfound that such proportions preserve the web while providing a usefulsilica pattern.

After application of the silica mixture, web 26 is passed through aheating oven 56 where the resulting silica pattern is heated to driveoff the organic solvents without heating web 26 to the point where heatdistortion of the cube-corner elements of the laminate will occur.

After drying, the silica is mechanically held to the cube-cornerelements on the reverse face 30 of web 26 by, it is believed,electrostatic forces and physical inter-engagement of the silicaparticles themselves.

Thus, as web 26 exits mixture application station 48, it has taken onthe form of a first modified laminate 58, i.e., a web 26 havingcube-corner elements with a precisely formed pattern of silica mixturescreened thereon over a portion of the elements, with an uncoveredportion of the cube-corner elements still exposed. As modified laminate58 exits drying over 56, it takes on a second modified laminateconstruction 60 wherein the solvents present in the silica mixture havebeen driven off and the silica itself has remained dried into itsscreened-on pattern.

The second modified laminate 60 then enters a backcoating applicationstation 62. The application of a water-based backcoating accomplishesseveral results. First, those areas onto which no silica has beenscreened or deposited will allow direct contact between the backcoatingand the reverse side 30 of the embossed or otherwise formedthermoplastic web 26, thus "wetting" web 26 with the liquid backcoatingmixture. Second, a layer of backcoating material will overlay the silicapattern formed on thermoplastic web 26 and, when applied effectively,will not disturb or disrupt the printed or screened-on silica pattern.Third, the backcoating may then be dried and/or cured to provide firmattachment to thermoplastic web 26 to provide a flat, smooth andintegral surface upon which further layers, such as a layer of pressuresensitive or heat-activated adhesive may be effectively and convenientlyapplied, and to protectively cover or encapsulate the silica pattern. Asurprising and unexpected result is that the silica prevents permeationof the liquid backcoating to the cube-corner pattern. As describedabove, such permeation would adversely affect the reflectivity of thefinal assembled laminate.

Application of the backcoating mixture to the second modified laminate60 may be accomplished in a number of ways, such as by spraying, rollerapplication, squeegeeing, or the like. The manner in which the backcoatis applied will be determined by, inter alia, the precise formulation ofthe backcoat and the pressure, or force, which can be withstood by thesilica pattern after it has been dried.

For purposes of illustration, a backcoating application station 62 maybe characterized as having a supply header or tank 64 communicating withan application means 66 which may be a nozzle or series of nozzles, orthe like. An implement such as a doctor blade 68 may be used to moreuniformly spread the backcoating after it has been applied withoutdamaging the silica pattern. A platen 70 provides support for the secondmodified laminate 60 during application of the backcoat.

After application, the third modified laminate 72 enters drying oven 74wherein the backcoat material is heat-cured, resulting in backcoatinglayer 32 as shown in FIG. 1.

Successful use of a backcoating requires that the backcoatingformulation meet several particularly important working parameters. Oneis that the backcoating have flow characteristics such that therelatively narrow and shallow runners formed by the silica pattern willbe filled, while not dewetting or disturbing the dried silica patternitself. This means that the viscosity of the backcoating must becarefully controlled to assure that the backcoating can be applied whilecompletely encapsulating the dried silica without disturbing the silicapattern. Another characteristic is that the backcoating cannot penetrateor interact with the applied silica to reach the interface between thesilica and the cube-corner pattern. Yet another requirement is that thebackcoating, when dried, have the required flexibility and toughness towithstand use in a laminate. Ideally, the backcoating would also be of acolor which enhances daytime visibility of articles made with suchlaminates.

Several preferred backcoatings have been utilized. Each may becharacterized generally as including a water-borne or water-basedpolymeric mixture or system, a whitening agent, a defoamer, a thickenerfor use in adjusting the final viscosity, and a pH-adjusting component.

A first preferred formulation of a backcoating is presented herewith asExample 1:

EXAMPLE 1

    ______________________________________                                        1.    DP-101, a water-borne polymeric                                                                   70% to 90%                                                system consisting of about 34%                                                                    by weight                                                 acrylic/urethane copolymer,                                                   60% water and 5% coalescent                                                   solvent, such as M-pyrol                                                2.    UCD-1060Q, a pre-dispersed                                                                         6% to 24%                                                coloring agent (titanium                                                      dioxide) containing about                                                     72% solids                                                              3.    BYK-W, a defoamer   0.4% to 0.9%                                        4.    TT 615 (50 percent in                                                                             1.5% to 3.5%                                              water) acrylic/based                                                          thickener to adjust viscosity                                           5.    De-ionized water (anti-skinning                                                                   None to 5%                                                and flow adjusting agent)                                               6.    Ammonia (28 percent aqueous                                                                       None to 0.3%                                              solution) to adjust pH to                                                     8.5 to 10.0                                                             ______________________________________                                    

The foregoing mixture is formed by adding the defoamer to thewater-borne acrylic/urethane copolymer system with gentle stirring.Thereafter, the coloring agent and the ammonia, if necessary, are addedas gentle stirring is continued. The thickener is thereafter added withincreasing blade speed and the entire mixture is stirred for about 30minutes at moderate speed. A preferred mixer for such an operation ismanufactured by Meyers Engineering of Bell, Calif. under the trade ormodel designation "550."

One preferred formulation used is blended as follows:

    ______________________________________                                        DP-101         80.7% by weight                                                UCD-1060Q      11.6                                                           TT 615         2.1                                                            BYK-W          0.5                                                            Deionized Water                                                                              4.2                                                            Ammonia        as needed                                                      ______________________________________                                    

DP-101 is a trade designation of Polyvinyl Chemical Industries, Inc. ofWilmington, Mass. While the precise formulation is not known, PolyvinylChemical Industries has assigned the trade designation DP-101 only tothe particular urethane/acrylic copolymer resin utilized in theforegoing backcoat formulation. UCD-1060 is a trade designation of theUniversal Color Dispersion Company on Lansing, Ill., used to identify adispersion product for water-based systems. DYK-W is a defoamermanufactured by Mallinckrodt of Melville, N.Y. BYK-W is a defoamermanufactured by Mallinckrodt of Melville, N.Y. TT 615 is a tradedesignation of the Rohm and Haas Company and is an acrylic-basedthickening agent. M-pyrol is a trade designation of the G.A.F.Corporation used to identify a methylpyrolidine coalescent solvent. Theamount of organic coalescent in the water based systems preferablyshould not exceed about 10% by formula weight, otherwise the backcoatingmight permeate the hydrophobic granular matter into the formedcube-corner pattern.

A second formulation for the backcoating mixture adds a cross-linkingagent to improve durability. After the ingredients of Example 1 havebeen mixed, and immediately prior to application, a quantity of theforegoing mixture is placed in a mixing vessel, and a freshly preparedsolution of cross-linking agent is mixed therewith. A preferredcross-linking agent generally is a polyfunctional aziridine, such asCX-100, manufactured by Poyvinyl Chemical Industries, Inc. ofWilmington, Mass. A preferred preparation consists of 35 lbs. ofbackcoating mixture combined with 150 grams of CX-100, dissolved in 150grams of water. The cross-linking agent is added in a proportion ofabout 0.5% to 1.5%, by weight, of constituents 1 through 4 of Example 1.

The resulting backcoating may be applied in a single pass, or insuccessively applied layers. If, for example, two passes are used, ithas been found advantageous to include about 0.5% of the cross-linkingagent in the first pass, with the backcoating of the second passcontaining about 1% of the cross-linking agent. After drying, the firstpass will have produced a construction that is 11/2-2 mils thick while,after the second pass, the total thickness will be 21/2-3 mils thick.

In a preferred embodiment, the before-and-after composition of thecross-linked backcoating are as follows:

    ______________________________________                                                  Slurry     After Drying                                             ______________________________________                                        DP-101      80.7% by weight                                                                            73.7% by weight                                      UCD-1060Q   11.6         21.6                                                 BYK-W       0.5          1.3                                                  TT 615      2.1          0.8                                                  De-ionized  4.2          Trace to none                                        water                                                                         CX-100      1.0          2.6                                                  ______________________________________                                    

In this embodiment, the addition of the cross linking agent enhances theweatherability of the finished laminate by increasing the durability andtoughness of the backcoating.

A second formulation of the backcoating material is herewith presentedas Example 2.

EXAMPLE 2

    ______________________________________                                        1.     Emulsion E-1829, a water-                                                                      42.1% to 62.1%                                               borne polymeric acrylic                                                                        by weight                                                    emulsion                                                               2.     Water             2.2% to 12.2%                                        3.     Ethylene glycol, an                                                                            1.5% to 2.5%                                                 anti-skinning flow                                                            improvement agent                                                      4.     UCD 1060Q, a pre-                                                                              26.2% to 36.2%                                               dispersed coloring                                                            agent (titanium                                                               dioxide)                                                               5.     Syloid 169, silicone                                                                           3.2% to 5.2%                                                 dioxide flatting agent                                                        to prevent blocking                                                    6.     Dimethylamino ethanol                                                                          0.3% to 0.5%                                                 pH-adjusting solvent                                                   7.     Balab 3017A defoamer                                                                           0.6% to 1.0%                                          8.     Texanol solvent, a                                                                             1.4% to 1.6%                                                 coalescent solvent for                                                        improved film formation                                                9.     TT 615 (50 percent in                                                                          None to 1.6%                                                 water) acrylic-based                                                          thickener to adjust                                                           viscosity                                                              ______________________________________                                    

The foregoing backcoating is prepared by adding the defoamer to thewater-borne system with gentle mixing, then adding the water, theanti-skinning agent, the pre-dispersed whitening agent and the aminewhile continuing gentle mixing. Thereafter, the coalescent solvent isadded. Blade speed is then increased and the thickener is added toadjust the viscosity to the desired level and the resulting mixture isthen stirred at moderate speed for 30 minutes.

Emulsion E-1829 is a trade designation of the Rohm and Haas Company ofPhiladelphia, Pa., for an acrylic emulsion vehicle. Syloid is a tradedesignation of the Davidson Checmical Company, a division of W. R.Grace, of Baltimore, Md. for a silicon dioxide flatting agent. Texanolis a trade designation of the Eastmlent Chemical Products Company ofKingsport, Tenn. used to identify a coalescing agent. Balab 3017-A is aproduct of the Organics Division of Witco Chemical Corporation, NewYork, N.Y.

Referring now to FIG. 2, a partial sectional view of a schematic portionof embossed thermoplastic web 26 after application of both silica 34 andbackcoating 32 is shown. As therein seen, reverse side 30 ofthermoplastic web includes a series of valleys, indicated generally at76. The valleys 76 schematically represent the cube-corner elementsfound in web 26 when the cube-corner pattern shown in FIG. 1 is embossedonto thermoplastic web 26. When the silica layer 34 is applied, thevalleys 76 between adjacent cube-corner elements are filled (exceptwhere the screen pattern leaves web 26 exposed) and, in a preferredembodiment of the invention, enought silica 34 is applied to extend adistance of about 0.0001 to about 0.003 inch above the embossed surfaceof thermoplastic web 26, as characterized by dimension A of FIG. 2. Inlike fashion, the backcoat layer 32 is applied to a thickness B of about0.002 to about 0.004 inch above the silica layer 34. Where runners orpaths 42 are formed, each such runner consists of the backcoat materialwhich extends downward to wet the floor of each valley 76 to a totaldepth C, as shown in FIG. 2 which, preferrably, is about 0.006 inch. Ina preferred embodiment of the present invention, each such runner is0.001 inch deep and, as characterized by dimension D in FIGS. 2 and 6,may be on the order of 0.015 inch wide.

In the embodiment herein illustrated, each discrete element of theapplied silica pattern is square in shape with the length of each sideof the square characterized by dimension E in FIGS. 2 and 6. Ashereinabove described, the percentage of surface area available forretroreflection may be adjusted by adjusting the dimensions D and E asshown in FIGS. 2 and 6. Where, for example, dimension D is 0.015 inchand dimension E is 0.200 inch, the effective surface available forretroreflection is 84 percent. Where dimension D is 0.027 inch anddimension E is 0.138 inch, approximately 70 percent of the surface ofthe resulting sheet preserves retroreflective characteristics. With adimension D of 0.029 inch and a dimension E of 0.096 inch, approximately55 percent of the total surface of the resulting sheet retainsretroreflective properties. In a preferred embodiment, dimension D is0.030 inch and dimension E is 0.170 inch to give an effective area ofreflection of about 73%.

Thus, the degree to which the resulting laminar sheet returns incidentlight towards its source may be adjusted independent of the actualcube-corner type pattern formed on thermoplastic web 26, in a mannerwhich is much more convenient and efficacious than changing the molddimensions or characteristics used to produce the embossed cube-cornerpattern.

Referring again to FIGS. 1 and 4, after fourth modified laminate 84exits drying oven 74, a pressure-sensitive or heat-activated adhesivelayer 36 may then be applied by taking the resulting laminate 84 anddrawing it past a station where a backing or release sheet 38,pre-coated with adhesive 36, may be layered directly onto backcoating38, resulting in a completed laminate 22 as shown in FIG. 1. Finally, ifa carrier sheet is used, it is stripped away, exposing obverse face 28as the light-receiving surface of the finished laminate 22.

It should be noted that the foregoing examples and preferred embodimentshave been presented with respect to a cube-corner embossed patternhaving a depth characterized by dimension X in FIG. 2 of 0.004 inch. Itis contemplated that patterns of varying depth and varying dimensionsmay be utilized, and that the dimension herein discussed for the depthof silica applied, and the width and depth of the runners therebyformed, may be varied without departing from the spirit and scope of theinvention as herein discussed.

The finished sheet will have the physical characteristics enabling it tosubstantially meet specification FP-79 for reflective sheeting, and itsreflective properties can easily be varied by utilizing different screenpatterns. Moreover, the coloring achieved by the existing laminatebackcoating substantially enhanced the daylight esthetics of thefinished material. The heating of the laminate during the drying andcuring of the silica, backcoating or adhesive, also may have an effecton the final reflective performance of the laminate, dependent upon thecharacteristics of the tools and the material chosen for the film. Ithas been determined that for optimum performance, the laminate shouldnot be heated above 180° F. during these various processing steps forthe preferred embodiment disclosed herein.

It may also be noted that while the silica pattern herein presented is aseries of squares turned to present a diamond-like pattern, other cellsizes and shapes are also possible, wherever they appear efficacious forpurposes of performance or appearance, and are within the spirit andscope of the invention as herein discussed and claimed.

As previously noted, FIG. 7 illustrates another preferred embodiment ofthe present invention. In this embodiment, a layer 25 of a more weatherresistant thermoplastic material than that forming web 26, such as UVmodified or impact modified polymethyl methacrylate, or a combinationthereof, is laminated to the impact modified acrylic forming web 26. Inits preferred form, layer 25 will be about 1.7 mil and will not exceed2.3 mil in thickness. It has been found that this added layer providesadditional weathering characteristics needed for certain environmentswhich, when not exceeding the noted thickness, permits the totallaminate to remain sufficiently flexible. Preferred materials in thisembodiment may be those sold under the trade designation VO52 or VO44 bythe Rohm & Haas Company, or a polyarylate sold under the tradedesignation Ardel, by Union Carbide. Various techniques may be employedto apply this outer layer to the web before the silica and backcoatingis applied. For example, the additional layer of thermoplastic materialmay be applied to solvent casting or may be co-extruded with the initialfilm.

A preferred formulation for the outer layer 25 includes use of Korad-D,the trade name of a modififed polymethyl methacrylate manufactured byPolymeric Extruded Products, Inc. of Newark, N.J. Such material includesU.V. light absorbing substances, and is cross-linked to a flexible,rubber base substance, adding flexibility. In particular, use ofTinuvin®234, a benzotriazol compound manufactured by Geigy, is used as aUV inhibitor. This substance is known chemically as2-(2H-benzotriazol-2-yl)-4-methyl-phenol. Korad D thermoplastic isdescribed in U.S. Pat. No. 3,562,235, issued on Feb. 9, 1971.

When Korad D thermoplastic is used, it may be applied as a 2 mil outerlayer during the cube forming process, or it may be co-extruded with theweb 26 before such formation, in a layer 1 mil thick, or it may beapplied in solution directly to the web 26 in a layer 1/2 mil thick. Theparticular thickness will depend in part on the total thicknessparameters of the finished laminate.

While the foregoing has presented various specific preferredembodiments, it is to be understood that these embodiments have beenpresented by way of example only. It is expected that others willperceive differences which, while varying from the foregoing, do notdepart from the spirit and scope of the invention as herein claimed anddescribed.

What is claimed is:
 1. A flexible retroreflective cube corner typelaminate sheet construction including a thermoplastic web with alight-receiving and transmitting first side and a second sidecoextensive with said first side, and a cube corner type retroreflectivepattern formed on at least a portion of said second side, saidconstruction comprising:a layer of hydrophobic granular materialdeposited on said second side to cover selected portions of said formedcube corner retroreflective pattern with remaining portions of saidsecond side devoid of said hydrophobic granular material; and a layer ofbackcoating material deposited on said second side to substantiallycompletely overly said hydrophobic granular material without disturbingthe pattern formed by said granular material, said backcoating materialsubstantially fully contacting said portions of said second side devoidof said granular material and being fixedly secured thereto, therebyencapsulating said hydrophobic granular material between said secondside and said backcoating layer, the particle size of said hydrophobicgranular material being such that the area in which it is deposited willbe effectively impervious to said backcoating material whereby saidbackcoating material is unable to penetrate said granular material andinteract with said second side except in the area devoid of saidgranular material.
 2. The construction of claim 1, wherein saidhydrophobic granular material is deposited so as to form a well-definedregular and repeating array.
 3. The construction of claim 1, whereinsaid hydrophobic granular material is deposited so as to form adiscrete, regularly-spaced array of pattern elements,each said patternelement being surrounded by contiguous portions of said second sidedevoid of said granular material.
 4. The construction set forth in claim3, in which said array of elements repeats itself in regular intervals.5. The construction of claim 1, wherein said hydrophobic granularmaterial is hydrophobic silica.
 6. The construction of claim 1, whereinsaid hydrophobic granular material has a primary particle size of about18 nanometers.
 7. The construction of claim 1, wherein said hydrophobicgranular material is hydrophobic silica.
 8. The construction of claim 1,wherein said backcoating consists essentially of a polymeric orcopolymeric, water-based system.
 9. The construction of claim 8, whereinsaid backcoating includes a major proportion of an acrylic/urethanecopolymer.
 10. The construction of claim 8, wherein said backcoatingincludes a major proportion of a polymeric acrylic water-borne system.11. The construction of claim 8, wherein said backcoating comprises anacrylic/urethane copolymer, a coloring agent, and an acrylic-basedthickening agent.
 12. The construction of claim 11, wherein saidbackcoating includes a defoaming agent.
 13. The construction of claim 8,wherein said backcoating comprises a polymeric acrylic system, acoloring agent, and a thickening agent.
 14. The construction of claim 8,wherein said backcoating comprises an acrylic/urethane copolymer, acoloring agent, a thickener and a cross-linking agent.
 15. Theconstruction of claim 14, wherein said backcoating includes a defoamingagent.
 16. The construction of claim 15, wherein said backcoating, whendried, comprises of about the following constituents by weight: 73.7%acrylic/urethane copolymer; 21.6% coloring agent; 0.8% thickening agent;1.3% defoaming agent; and 2.6% cross-linking agent.
 17. The constructionof claim 1, further including a lamina of flexible thermoplasticmaterial co-extensive with and secured to said light-receiving andtransmitting side of said thermoplastic web,said lamina including meansfor absorbing radiation in about the ultraviolet range.
 18. Theconstruction of claim 17, wherein said lamina is formed from polymethylmethacrylate in a thickness from about 0.2 mil to 0.4 mil.
 19. Theconstruction of claim 17 wherein said lamina is formed from arubber-based cross-linked thermoplastic acrylic polymer composition,andsaid absorbing means is 2-(2H-benzotriazol-2-yl)-4-methyl-phenol. 20.The construction of claim 19, wherein said lamina is from about 0.5 milto about 2.3 mil in thickness.
 21. The construction of claim 1, furtherincluding a lamina of flexible thermoplastic material co-extensive withand secured to said light-receiving and transmitting side of saidthermoplastic web,said lamina including a rubber-based cross-linkedthermoplastic acrylic polymer composition.
 22. A retroreflective cubecorner laminate sheet construction comprising:a thermoplastic web havinga light-receiving and transmitting first side, and a second sidecoextensive with said first side; said second side having a repeatingretroreflective cube corner pattern formed on at least a portionthereof; a layer of hydrophobic granular material disposed on saidsecond side to cover selected portions of said formed cube cornerpattern and leaving remaining area of said second side devoid of saidhydrophobic granular material; a layer of backcoating material depositedon said second side to overlay said hydrophobic granular material; saidbackcoating material also contacting substantially all of said remainingarea of said second side devoid of said hydrophobic granular material;the particle size of said hydrophobic granular material being such thatthe area in which it is deposited will be effectively impervious to saidbackcoating material, whereby said backcoating material is unable topenetrate said granular material and interact with said second sideexcept in said remaining area devoid of said granular material; saidbackcoating material being in secure attachment to said second side atsaid remaining area, thereby encapsulating said granular materialbetween said second side and said backcoating material; a layer ofadhesive applied to and generally co-extensive with said backcoatingmaterial; and a release sheet releably secured to said adhesive layer.23. The construction of claim 22, wherein said hydrophobic granularmaterial is deposited on said second side so as to form a regular andrepeating array.
 24. The construction of claim 23, wherein said arrayincludes discrete, regularly-spaced pattern elements of selectedgeometric shape; andeach said pattern element is surrounded bycontiguous portions of said second side devoid of said hydrophobicgranular materials.
 25. The construction of claim 24, wherein said arraycomprises an array of square pattern elements;said pattern elementsdefining therebetween a series of paths devoid of said hydrophobicgranular material.
 26. The construction of claim 22, wherein saidhydrophobic granular material has a particle size of about 18 nanomters.27. The construction of claim 22, wherein said hydrophobic granularmaterial is hydrophobic silica.
 28. The construction of claim 22,wherein said backcoating includes a major proportion of a water-borneacrylic-urethane copolymer.
 29. The construction of claim 22, whereinsaid backcoating includes a major proportion of a polymeric acrylicwater-borne system.
 30. The construction of claim 24, wherein saidhydrophobic granular material is hydrophobic silica.
 31. Theconstruction of claim 22, further including a lamina of flexiblethermoplastic material co-extensive with and secured to saidlight-receiving and transmitting side of said thermoplastic web,saidlamina including means for absorbing radiation in about the ultravioletrange.
 32. The construction of claim 31, wherein said lamina is formedfrom a rubber-based cross-liked thermoplastic acrylic polymercomposition, andsaid absorbing means is2-(2H-benzotriazol-2-yl)-4-methyl-phenol.
 33. The construction of claim40, wherein said lamina is from about 0.5 mil to about 2.0 mil inthickness.
 34. The construction of claim 22, wherein said lamina isformed from polymethyl methacrylate in a thickness from about 0.2 mil to0.4 mil.
 35. A method for producing a cube corner type retroreflectivelaminate sheet construction, said method comprising the steps of:(a)applying a layer of hydrophobic granular material to a web ofthermoplastic material having a retroreflective cube corner formedpattern on at least a portion of one side, said granular materialdeposited so as to form a regular and repeating array on saidretroreflective pattern; (b) forming, as part of said array a pluralityof paths on said one side devoid of said hydrophobic granular material;(d) applying a layer of backcoating material to overlay said hydrophobicgranular material and to fill said paths; and (d) adhering saidbackcoating material to encapsulate said hydrophobic granular materialbetween said formed side and said backcoating material,the particle sizeof said hydrophobic granular material being such that the area in whichit is deposited will be effectively impervious to said backcoatingmaterial whereby said backcoating material is unable to penetrate saidgranular material and interact with said second side except in the areadevoid of said granular material.
 36. The method of claim 35 whereinsaid layer of hydrophobic granular material consists initially of aslurry comprising a hydrophobic granular material, a polar solvent, anda non-polar solvent, said polar solvent and said non-polar solventpresent in relative proportions sufficient to allow deposition of saidhydrophobic granular material in said well-defined array on saidthermoplastic web.
 37. The method of claim 36, wherein said polarsolvent is an aliphatic alcohol.
 38. The method of claim 36, whereinsaid polar solvent is n-butanol.
 39. The method of claim 36, whereinsaid non-polar solvent comprises low odor mineral spirits.
 40. Themethod of claim 36, wherein said polar solvent is present in an amountfrom about 10% to about 30% of said slurry, and said non-polar solventis present in an amount from about 40% to about 70% of said slurry. 41.The method of claim 36, wherein said polar solvent is present in anamount of about 15% of said slurry.
 42. The method of claim 36, whereinsaid slurry consists of from about 15% to about 35% of said hydrophobicgranular material, from about 10% to about 30% of said polar solvent,and from about 40% to about 70% of said non-polar solvent.
 43. Themethod of claim 36, wherein said slurry includes a thixotropicthickener.
 44. The method of claim 35 wherein said backcoating consistsof the following constituents:(a) a water-borne mixture of anacrylic/urethane copolymer in a proportion from about 70 perent to about90 percent; (b) a coloring agent in a proportion from about 6 percent toabout 24 percent; (c) a defoamer in a proportion from about 0.4 percentto about 0.9 percent; (d) an acrylic-based thickening agent in aproportion from about 1.5 percent to about 3.5 percent; (e) deionizedwater in a proportion from none to about 5 percent; and (f) apH-adjusting agent in a proportion from none to about 0.3 percent. 45.The method of claim 44, wherein said backcoating includes:(g) an aqueoussolution of a cross-linking agent in a proportion from about 0.5 percentto about 1.5 percent, by weight, of constituents (a)-(d).
 46. The methodof claim 35, wherein said backcoating consists of the followingconstituents:(a) a water-borne polymeric acrylic system in a proportionfrom about 42 percent to about 62 percent; (b) water in a proportionfrom about 2 percent to about 12 percent; (c) an anti-skinning agent ina proportion from about 1.5 percent to about 2.5 percent; (d) a coloringagent in a proportion from about 5 percent to about 36 percent; (e) aflatting agent in a proportion from about 3 percent to about 5 percent;(f) a pH-adjusting agent in a proportion from about 0.3 percent to about0.5 percent; (g) a defoamer in a proportion from about 0.6 percent toabout 1.0 percent; (h) a coalescent solvent in a proportion from about1.0 percent to 1.6 percent; and (i) a thickener in a proportion from 0percent to 3.6 percent.
 47. The method of claim 35, wherein said slurryincludes a polar solvent and a non-polar solvent.
 48. The method ofclaim 47, wherein said polar solvent is an aliphatic alcohol.
 49. Themethod of claim 47, wherein said polar solvent is n-butanol.
 50. Themethod of claim 47, wherein said non-polar solvent comprises low odormineral spirits.
 51. The method of claim 35, further including the stepof:(e) securing an overlayer of weather-resistant thermoplastic materialcontaining absorbers of radiation in about the ultra-violet range, tothat side of said web opposite to the side on which said cube cornertype pattern is formed.
 52. The method of claim 35, interposing betweensteps (b) and (c) the step of:(b₁) drying said layer of hydrophobicgranular material.
 53. The method of claim 35, wherein said hydrophobicgranular material is hydrophobic silica.
 54. The method of claim 35,wherein substantially said entire second side is formed to contain cubecorner elements therein and said backcoating adheres directly toportions of said cube corner elements devoid of said hydrophobicgranular material.
 55. A flexible cube corner type retroreflectivelaminate sheet construction including a retroreflective web with alight-receiving and transmitting first side and a second sideco-extensive with said first side, and a cube corner typeretroreflective pattern formed on at least a portion of said secondside, said construction comprising:a layer of hydrophobic granularmaterial deposited on said second side to cover selected portions ofsaid cube corner pattern, with the uncovered portions of said secondside forming paths devoid of said granular material; a layer ofbackcoating material deposited on said second side to overlay saidhydrophobic granular material, said backcoating material contacting saiduncovered portions of said cube corner pattern on said second side andbeing fixedly secured thereto, thereby encapsulating said granularmaterial between said second side and said backcoating layer, theparticle size of said hydrophobic granular material being such that thearea in which it is deposited will be effectively impervious to saidbackcoating material wherein said backcoating material is unable topenetrate said granular material and interact with said second sidepattern except in said uncovered portions; and said paths being sizedand shaped to cover a selected portion of the surface area of said cubecorner pattern found in said second web side thereby to control theamount of incident light reflected from said first side of saidretroreflective web, without changing said formed cube corner pattern onsaid second side.
 56. The construction of claim 55, wherein saidhydrophobic granular material is deposited so as to form aregularly-spaced array of discrete pattern elements,each said patternelement being surrounded by contiguous portions of said paths.
 57. Theconstruction of claim 56, wherein said pattern elements are square. 58.The construction of claim 56, wherein each said pattern element is asquare having sides of 0.200 inch and each said path is 0.015 inch wide.59. The construction of claim 56, wherein each said pattern element is asquare having sides of 0.138 inch wide and each said path is 0.127 inchwide.
 60. The construction of claim 56, wherein each said element is asquare having sides of 0.096 inch and each said path is 0.029 inch wide.61. The construction of claim 56, wherein each said pattern element is asquare having sides of 0.170 inch wide and each said path is 0.030 inchwide.
 62. The construction of claim 55, wherein said paths definerectangular pattern elements.
 63. The construction of claim 55,including a lamina co-extensive with and secured to said first side ofsaid retroreflective web,said lamina including means to absorb radiationin about the ultraviolet range on said retroreflective web.
 64. Theconstruction of claim 63, wherein said lamina is formed of polymethylmethacrylate in a thickness of about 0.2 mil to about 0.4 mil.
 65. Theconstruction of claim 63, wherein said lamina is formed from arubber-based, cross-linked thermoplastic acrylic polymer composition.66. The construction of claim 63, wherein said absorbing means is2-(2H-benzotriazol-2-yl)-4-methyl-phenol.
 67. The construction of claim1, 22 on 55, wherein substantially the entire second side is formed tocontain cube corner elements therein and said backcoating adheresdirectly to portions of said cube corner elements devoid of saidhydrophobic granular material.